1. Technical Field
This invention relates to a light projecting and receiving unit for use in a human body detecting apparatus for automatic door, and more particularly to a light projecting and receiving unit having a light projecting section and a light receiving section, each of the sections consisting of a plurality of split concave mirrors combined with one another to have a common or the same focus.
2. Description of the Prior Art
As for the human body detecting apparatus for use in automatic doors, there has so far been known and employed an active type human body detector apparatus adapted to detect the entry of the human body into the human body detection range by allowing the light beams projected by a light projector and reflected by the human body to be received by a light receiver.
Regarding a light projector and a light receiver for use in such a human body detector apparatus, a combination of concave mirrors with light projecting elements and concave mirrors with light receiving elements has been known, which is arranged such that the light beams emanated by the light projecting elements having a low photo-output can be irradiated as spot light beams of acute directional property, and the light beams reflected by the human body when subjected to the spot light can be detected by the light receiving elements.
In the above-mentioned publicly known prior art light projector and light receiver, the human body detection range is determined by the range of irradiation of spot light emanated by the light projector, i.e., the number of the spot light beams. Therefore, in order to obtain a wide range of detection of the human body, a multiplicity of spot light beams are required so that provision of a large number of combinations of light projecting elements with concave mirrors as well as the corresponding number of combinations of light receiving elements with concave mirrors is necessarily required. Accordingly, both the light projector and the light receiver become large-sized, thus increasing the manufacturing cost thereof and the space required for installation thereof. These are disadvantages in the previously produced active type human body detection apparatus.